1. Technical Field
The present invention relates to liquid ejection heads and liquid ejection apparatuses.
2. Related Art
JP-A-2009-172878 and JP-A-2009-196329 disclose a liquid ejection head including a substrate in which a pressure generating chamber that communicates with a nozzle opening for ejecting liquid is formed, and a piezoelectric element having a piezoelectric layer, a lower electrode that is formed on the lower side of the piezoelectric layer and an upper electrode that is formed on the upper side of the piezoelectric layer. In such a liquid ejection head, the lower electrode is provided as an individual electrode that corresponds to each of the pressure generating chambers, and the upper electrode is provided as a common electrode for a plurality of piezoelectric elements that correspond to a plurality of pressure generating chambers.
The above-mentioned piezoelectric element displaces when a voltage is applied across both electrodes and flexes into the pressure generating chamber. During flexing, a significant amount of stress is generated at the interface between an area on the piezoelectric element where the upper electrode, the piezoelectric layer and the lower electrode overlap (active section) and an area other than the active section (inactive section), which causes distortion to be concentrated at this position. Since concentration of distortion may cause a problem such as crack in the piezoelectric layer that forms the piezoelectric element, it has been required to prevent such a problem. Further, in addition to prevention of the above-mentioned problem, it has been also required to increase the amount of liquid to be output (ejected) from the pressure generating chamber to the outside of the nozzle opening by using deformation of the vibration plate in response to flexing of the piezoelectric element, thereby improving performance of the liquid ejection head.